(i) Field of the Invention
This invention relates to scaffolding systems, and more particularly to a pole jack for travelling up and down a pole for supporting a scaffold.
(ii) Description of the Related Art
In numerous industries, it is necessary to erect scaffolding both for internal use as well as for external use in order to permit workers to stand at an elevation above ground surface. Typically, by way of example, a scaffolding system is utilized in the installation of aluminum siding on the exterior of housing. Such scaffolding is conventionally erected by utilizing pump jack poles which are spaced apart and secured in spaced relationship to a house by means of braces. Pump jacks are used to ride up and down the poles. The pump jacks typically include support arms on which are extended scaffold staging. The workers can stand on the scaffold staging and operate the pump jacks to move the staging up and down along the pump jack poles.
U.S. Pat. No. 4,597,471 discloses a heavy duty pump jack which includes a frame with upper and lower shackle members supported by the frame. A pump arm is pivotally provided on the frame and operates the shackles in alternating relationship. The pump arm serves to position the upper shackle in a twist gripping securing relationship on the pole while it then serves to raise the frame stepwise upwardly along the pole. The weight of the jack then shifts so that the lower shackle twist grips the pole and the upper shackle steps up to a next position on the pole. In this manner, the non-gripping shackle steps up the pole while the opposing shackle grips the pole. To ride the pump jack down the pole, the lower shackle is released from its gripping relationship and the upper shackle is rolled down the pole by means of a handle.
U.S. Pat. No. 4,382,488 describes a pump jack pole formed of elongated hollow metal with a rubberized surface on one side of the pole. Such poles were found to be strong, long lasting and easier to manipulate than the standard wooden poles. U.S. Pat. No. 4,463,828 and aforementioned U.S. Pat. No. 4,597,471 describe improved pump jacks which include features to improve the safety of the pump jack as well as its strength. Such features include the ability to release one of the shackles by means of a foot release pedal, thereby avoiding the necessity of bending over and releasing the lower shackle by hand. It is also known to employ an over-the-center spring loaded handle to control the rolling down of the pump jack.
The aforementioned features provided in pump jacks have served to improve the operation and safety of such pump jacks in the industry. Nevertheless, additional safety measures are always warranted with respect to this type of scaffold system. For example, the known spiral rod utilized to control rolling down of the pump jack along the pump jack pole has a tendency to wear, thereby causing accidental sliding of the pump jack down the pole. Additionally, as the spiral rod wears, it may have a tendency to snap outwardly, thereby further causing additional accidents.
While heretofore pump jacks and pump jack poles were typically utilized to support scaffolding in the installation of aluminum siding, such equipment can actually by utilized in other scaffolding sectors. For example, in industrial or marine use, scaffolding is often required both for internal use and external use. In warehouses, where access to various tiers of stored objects is required, the use of the pump jack and pump jack poles would be convenient. Platform and pallet staging could be raised and lowered in order to reach the desired objects. Similarly, in marine applications, the loading and unloading of ships could use the present pump jack and pump jack pole arrangement to advantage.
While utilizing the pump jack and pump jack pole for industrial use, however, additional strength would be needed for the pump jack in order to support the extra weight of the platforms. Such extra strength is required not only in the construction of the pump jack itself, but in the operative portions thereof, including the shackles, the platform, etc.
Accordingly, while the aforementioned prior art patents have provided improvements in the utilization of pump jacks and pump jack poles, all such systems are dependent on frictional engagement for climbing and for support.
Accordingly, it is a principal object of the present invention to provide an alternative to the use of pump jacks and pump jack poles dependant on friction for supporting scaffolding equipment.
Another object of the present invention is the provision of an improved primary pole jack having a positive interlock system to prevent accidental disengagement or slipping of the jack on the pole.
Still another object of the present invention is the provision of an improved jack which includes a simple directional selector arrangement for lowering the pole jack down the jack pole.
And a further object of the present invention is to provide a pole jack having an independent secondary locking system to engage the pole in the event of failure of the primary mechanism.